Don't allow trailing period in mention

Fixes #249

activities/models/post.py

@@ -342,7 +342,7 @@ class Post(StatorModel):
         PostTypeData.parse_obj(value)
 
     mention_regex = re.compile(
-        r"(^|[^\w\d\-_/])@([\w\d\-_]+(?:@[\w\d\-_]+\.[\w\d\-_\.]+)?)"
+        r"(^|[^\w\d\-_/])@([\w\d\-_]+(?:@[\w\d\-_\.]+[\w\d\-_]+)?)"
     )
 
     def linkify_mentions(self, content: str, local: bool = False) -> str:

tests/activities/models/test_post.py

@@ -77,6 +77,7 @@ def test_linkify_mentions_remote(
         local=True,
     )
     assert post.safe_content_remote() == "<p>@test@example.com, welcome!</p>"
+
     # Test case insensitivity (remote)
     post = Post.objects.create(
         content="<p>Hey @TeSt</p>",
@@ -89,6 +90,18 @@ def test_linkify_mentions_remote(
         == '<p>Hey <a href="https://remote.test/@test/">@test</a></p>'
     )
 
+    # Test trailing dot (remote)
+    post = Post.objects.create(
+        content="<p>Hey @test@remote.test.</p>",
+        author=identity,
+        local=True,
+    )
+    post.mentions.add(remote_identity)
+    assert (
+        post.safe_content_remote()
+        == '<p>Hey <a href="https://remote.test/@test/">@test</a>.</p>'
+    )
+
     # Test that collapsing only applies to the first unique, short username
     post = Post.objects.create(
         content="<p>Hey @TeSt@remote.test and @test@remote2.test</p>",